He has also been a motor mechanic, postman, public servant, real estate agent, small business owner and union organiser.

He provided more than 30 reports to the parliament affecting the business, environmental and residential planning of the capital.

Gentleman tabled and passed the gross feed-in-tariff for Canberra,[6] bringing the ACT to the forefront in renewable energy incentives.

As Minister for the Environment, Gentleman led reforms to outlaw destructive yabby traps[10] and oversaw the recovery plan for Namadgi National Park,[11] which was significantly damaged by bushfires in early 2020.

[12] Gentleman has been a public advocate for protecting Namadgi National Park from potential damage caused by feral horses.